In internal combustion engines, particularly in large installations such as are found with big marine diesels, engine wear and failure can result from several causes. Shaft misalignments can be produced by uneven forces applied to the external engine mounts forcing mounts to change in position and thus applying dangerous internal forces to the crank shaft. Bearing wear can also cause the crank shaft to experience forces of misalignment which can create premature engine failure. Similar measurements and monitoring is needed in other reciprocating apparatus, such as gas compressors.
Such engine conditions will result in changes in the maximum travel of the engine pistons at both top and bottom positions. Prior monitoring instruments for detecting these conditions have included break-away stems connected to pressurized fluid lines and positioned so as to break and release the fluid pressure whenever the piston bottom travel exceeds a preset tolerance, bringing the piston against the stem and snapping it off.
The break-away system tolerance must be set large enough so that activation of it, which of necessity involves engine shut down, does not occur until a significant change in piston bottom is experienced. Otherwise, too frequent engine shut downs would take place. The existence of a large tolerance, however, permits gradual changes in piston travel, indicative of effects that could be remedied in many cases, from being detected. Activation of the break-away detector also requires restoration of the break-away unit by expensive and time consuming repair work.